This invention relates to a process for the production of acetone by the catalytic, oxidative decarbonylation of isobutyraldehyde.
Isobutyraldehyde, obtained in very large amounts as an unavoidable by-product during the manufacture of n-butyraldehyde from propylene by the oxo synthesis, has heretofore been utilized almost exclusively only in power plants for its calorific value.
Many experiments have been conducted to find a more economical use for isobutyraldehyde. Thus, it is known to split isobutyraldehyde into its starting components, propylene, carbon monoxide, and hydrogen (DAS [German Published Application] No. 1,917,244) and to react isobutyraldehyde to obtain synthesis gas. See German Unexamined Laid-Open Application DOS No. 1,767,281. However, the economic value of these products is only minor. Furthermore, attempts have been made to convert isobutyraldehyde into valuable products by oxidation. It is known to react isobutyraldehyde in the liquid phase with oxygen-containing gases in the presence of metallic oxide dispersions of molybdenum, chromium, silver, nickel, vanadium, tungsten, titanium, cerium, manganese, or cobalt as the catalyst and in the presence of a liquid diluent, such as isobutyric acid or the 2-ethylhexyl ester of 2-ethylhexanecarboxylic acid or silicone oil, to produce acetone, isopropanol, and isobutyric acid, German Application DAS No. 1,956,018. However, in this process, the yield and selectivity are relatively low. An improved selectivity is obtained in a process described in DOS No. 2,157,307 (U.S. Pat. No. 3,804,902). In this method, isobutyraldehyde is oxidized to acetone in the gaseous phase with oxygen on a catalyst of manganese oxide and optionally an alkali metal oxide on activated aluminum oxide as the support. With a 93% isobutyraldehyde conversion, the yield of acetone is 85 molar percent, based on the converted isobutyraldehyde and with a 98% isobutyraldehyde conversion, the acetone yield is only 83 molar percent.
For an economical production of acetone, as nearly complete as possible isobutyraldehyde conversion is required because the volatility of acetone is similar to that of the isobutyraldehyde, making separation difficult. Another difficulty arises from high portions of unconverted isobutyraldehyde by the unavoidable oxidation to isobutyraldehyde with excess oxygen during condensation. Therefore, the acetone yields attained according to the above-described process are unsatisfactory, especially at a high isobutyraldehyde conversion. Also, due to the complete combustion of approximately one-fifth of the isobutyraldehyde, the yield of acetone is proportionately reduced. Additionally, the removal of the additional heat from the reactors becomes a technical problem of reaction, because of the very high heat of reaction for the total combustion of the isobutyraldehyde.
It is well known that the load on the catalyst, i.e., the quantity of isobutyraldehyde fed per unit time, must be adapted to the discharge possibilities for the heat of reaction to avoid temperature profiles which are too steep, because high peak temperatures reduce the selectivity of the oxidation. A reduction in total heat of combustion permits a correspondingly higher load on the catalyst and thus a higher space-time yield of acetone. For conducting the process on a large technical scale, the space-time yield, i.e., the amount of product obtainable per catalyst volume and time, is always of great importance.
Consequently, it is an object of this invention to provide a process for the production of acetone by the catalytic, oxidative decarbonylation of isobutyraldehyde at an elevated temperature in the gaseous phase, which has a very high selectivity with respect to the formation of acetone even at a very high isobutyraldehyde conversion, and thus has simultaneously a lower total combustion of isobutyraldehyde. Other objects will be apparent to those skilled in the art.